In the processing of poultry for human consumption there is a concern about the levels of salmonella bacteria on the poultry. Therefore, methods and apparatus which reduce the levels of salmonella bacteria are desired. However, the poultry producing industry is very competitive, and therefore, the apparatus and methods must be cost effective.
There are several steps which occur after slaughtering the poultry prior to packing and shipping. Poultry is processed, after slaughtering, by scalding to assist in defeathering, defeathering by machine, washing, eviscerating, and chilling prior to packing. One of the concerns in these treatments is to avoid causing a change in the appearance characteristics of poultry which would make the poultry unsalable.
While a large part of the carcass contamination with salmonella can be removed by water washing, there is still a concern with colonies of bacteria left behind which can cross-contaminate surfaces which are not heated sufficiently to cause thermal destruction of the bacteria.
It has been recognized that Whatever treatment system is used, it must be economical, easy to use, compatiblity with food manufacturing, and must not change the organoleptic properties of the poultry. One such method recognized for reducing salmonella is to treat the carcass with an eight (8) percent solution of trisodium phosphate having a pH of about 11.8, preferably during the inside/outside wash after evisceration. U.S. Pat. No. 5,283,073 discloses such a process and is incorporated herein by reference.
When a pure water wash was used, typically the water and the debris, such as pin feathers and fat globules, were sent down the sewer drain without an attempt to recycle the water. However, with the use of solutions such as trisodium phosphate and the increasing cost associated with water and the disposal of the waste, it has been desirable to filter the solution/debris mixture (herein referred to as the "mixture") in order to recycle the solution.
An existing method of filtering the mixture is to use a filter system which places the mixture in a centrifuge separator having a conveyor. The conveyor has a hub and one or more flights for rotating the mixture and imparting a centrifugal force on the mixture. A mesh screen filter encircles the conveyor, through which the solution passes and is filtered. The debris is moved by the flight of the conveyor to one end where the debris is removed and disposed. A centrifuge of this type is sold by Russell Finex.
In order to remove the feathers and fat globules and other debris which adheres to the filter and is not removed by the movement of the conveyor, the separator has a series of four pipes running laterally next to and outside of the filter. The filter is, therefore, interposed between the conveyor and the pipes. The pipes each have a series of nozzles for spraying a solution at the filter. In a known embodiment there are four nozzles per pipe. With the conveyor continuing to rotate but with the mixture not being pumped into the conveyor, the spray hits the exterior of the filter in order to force feathers and fat globules stuck to the interior of the filter away from the pores of the filter. The debris is moved by the conveyor. This is generally described as backwashing the filter. The system must be shut down in order to do the backwash, since the pressure of the mixture against the filter created by the centrifuge would not allow the spray from the exterior to remove debris from the filter.
Even with the system shut down, the backwash system described does not do a thorough job of cleaning the filter. The sixteen (16) nozzles do not effectively reach all areas of the filter. Even with the sixteen nozzles, a cone spray pattern was required to attempt to cover the majority of the filter screen surface. A cone pattern nozzle is limited as to the impact energy that the spray can deliver to a given target. Even at elevated pressures, the tendency of the cone spray pattern is to atomize the spray rather than increase impact energy. One of the major difficulties that results from the ineffective cleaning is that the filter gets clogged and the system must wastefully be shut done every 30 minutes to 2 hours and centrifuge pulled apart for a more thorough cleaning. This results in a system in which cost effectiveness is minimal, even with the improved reduction of salmonella contamination and potentially longer shelf life of the poultry which results from use of the trisodium phosphate solution.
It is desired to have a system, a backwash system, for sending a flow of fluid at the filter in the direction opposite the normal flow to remove the solids (i.e., debris) from the filter such that the centrifuge does not need to be torn apart specifically to de-clog the filter. In addition, it is desired that such a backwash system allow filtering to continue to occur while backwashing.